Fuel injection valve

ABSTRACT

A fuel injector ( 1 ), in particular an injector for direct injection of fuel into a combustion chamber of a mixture-compressing, spark-ignition internal combustion engine has a solenoid ( 10 ), which cooperates with an armature ( 20 ), and a magnetic internal pole ( 13 ) and a magnetic external pole ( 9 ), the armature ( 20 ) being connected in a force-locking manner to a valve needle ( 3 ) for actuating of the fuel injector ( 1 ), the valve needle having on its injection end a valve-closure member ( 4 ), which cooperates with a valve seat ( 6 ). At least one permanent magnet ( 34 ) is situated in a connecting area between the internal pole ( 13 ) and the external pole ( 9 ).

BACKGROUND INFORMATION

[0001] The present invention relates to a fuel injector according to the preamble of the main claim.

[0002] For magnetic throttling between the poles of an electromagnetically operable fuel injector, usually either a nonmagnetic intermediate component is used or the seat carrier or the valve casing is equipped with a thin-walled collar as a throttle, depending on the design of the fuel injector. The magnetic circuit rapidly approaches saturation in the throttle location due to the fact that the material has a small wall thickness.

[0003] For operation of high-pressure fuel injectors, a connecting element or a supporting ring is mounted around the throttle location to mechanically reinforce the resulting mechanically weak spot.

[0004] For example, German Patent Application 195 03 821 A1 describes a fuel injector in which the number of components of the valve tube is reduced so that the number of joints and connection points is also reduced. The entire valve tube is made of a magnetically conducting material, so that no nonmagnetic intermediate components are necessary. A thin-walled throttle point is provided between the core and the valve seat carrier.

[0005] One disadvantage of the known fuel injectors described above is in particular the mechanical weakening of the valve housing or the seat carrier at the location of the magnetic throttle. Since the fuel injectors are designed mainly for direct injection of fuel into the combustion chamber of internal combustion engines having fuel mixture compression and spark ignition, high pressures prevail in the combustion chamber as well as in the fuel injector, potentially damaging the fuel injector during operation.

[0006] The connecting components normally used to reinforce the housing have the disadvantage that they must be made of a nonferritic material, independently of the internal pole and the external pole. Assembly of the connecting components may also damage the housing, which is weak at this point.

ADVANTAGES OF THE INVENTION

[0007] The fuel injector according to the present invention having the characterizing features of the main claim has the advantage over the related art that the magnetic throttling is achieved by attaching permanent magnets to the connecting area, which is manufactured in normal thickness, between the internal pole and the external pole of the fuel injector. The permanent magnets create a primary flux in the ferritic material of the external pole, which makes available only a reduced cross section for the secondary flux generated by the solenoid.

[0008] Advantageous refinements of the fuel injector characterized in the main claim are possible through the measures characterized in the subclaims.

[0009] The possibility of selecting any desired number and spacings of the permanent magnets is advantageous. A single ring-shaped permanent magnet is especially simple to manufacture and easy to mount.

[0010] The various options for attaching the permanent magnets to the external pole are advantageous. Attachment through the magnetic force of the permanent magnets is especially advantageous.

[0011] A secure seating on the housing may be achieved by sheathing the assembled permanent magnets with a plastic sheath.

[0012] The permanent magnets are advantageously designed in the form of annular segments which are in contact with the housing due to a suitably selected radius of curvature.

[0013] The possibility of influencing the properties of the fuel injector through targeted magnetization of the permanent magnets after assembly is particularly advantageous.

[0014] Advantageous materials for manufacturing the permanent magnets include in particular substances having a high energy content, such as iron-neodymium-boron or compounds of cobalt with rare earth metals.

Drawing

[0015] One embodiment of the present invention is illustrated in simplified form in the drawing and explained in greater detail in the following description.

[0016]FIG. 1A shows a schematic section through an example of a fuel injector according to the related art,

[0017]FIG. 1B an enlarged schematic detail in area II in FIG. 1A,

[0018]FIG. 2 a longitudinal section through an embodiment of a fuel injector according to the present invention in the same area II as in FIG. 1B, and

[0019]FIG. 3 a section through the embodiment shown in FIG. 2 of the fuel injector according to the present invention along line III-III in FIG. 2.

DETAILED DESCRIPTION OF THE EMBODIMENT

[0020] Before describing an embodiment of a fuel injector 1 according to the present invention on the basis of FIGS. 2 and 3, the essential components of a fuel injector according to the related art which has the same design except for the measures according to the present invention will now be explained briefly for a better understanding of the present invention on the basis of FIG. 1.

[0021] Fuel injector 1 is designed in the form of a fuel injector for fuel injection systems of engines having fuel mixture compression and spark ignition. Fuel injector 1 is suitable in particular for direct injection of fuel into the combustion chamber (not shown) of an engine.

[0022] Fuel injector 1 is made of a nozzle body 2 in which a valve needle 3 is situated. Valve needle 3 is mechanically connected to a valve-closure member 4, which cooperates with a valve-seat surface 6 on a valve seat body 5 to form a sealing seat. In this embodiment, fuel injector 1 is an inwardly opening fuel injector 1 which has an injection orifice 7. Nozzle body 2 is sealed by a gasket 8 from external pole 9 of a solenoid 10. Solenoid 10 is encapsulated in a coil housing 11 and wound onto a field spool 12, which is in contact with an internal pole 13 of solenoid 10. Internal pole 13 and external pole 9 are separated from one another by a constriction 26 and are joined by a non-ferromagnetic connecting component 29. Solenoid 10 is energized by an electric current that may be supplied over an electric plug-in contact 17 via a line 19. Plug-in contact 17 is enclosed by plastic sheathing 18, which may be integrally molded on internal pole 13.

[0023] Valve needle 3 is guided in a disk-shaped valve needle guide 14. A matching adjusting disk 15 is used to adjust the lift. An armature 20 is situated on the other side of adjusting disk 15. Via a first flange 21, the armature is connected in a force-locking manner with valve needle 3, which is joined by a weld 22 to first flange 21. A restoring spring 23, which is pre-stressed by a sleeve 24 in the present design of fuel injector 1, is supported on first flange 21. Fuel channels 30 a through 30 c convey fuel, which is supplied through a central fuel feed 16 and is filtered through a filter element 25, to injection orifice 7, these channels running in valve needle guide 14, in armature 20 and on valve seat body 5. Fuel injector 1 is sealed from a fuel line (not shown) by a gasket 28.

[0024] An annular damping element 32 made of an elastomer material is situated on the injection side of armature 20. It sits on a second flange 31 which is connected in a force-locking manner with valve needle 3 via a weld 33.

[0025] In the resting state of fuel injector 1, armature 20 is acted upon by restoring spring 23 against its direction of lift, so that valve-closure member 4 is held in sealing contact on valve seat 6. When solenoid 10 is energized, it builds up a magnetic field which moves armature 20 in the direction of lift against the elastic force of restoring spring 23, the lift being predetermined by a working gap 27 between internal pole 12 and armature 20 in the resting position. Armature 20 also entrains first flange 21, which is welded to valve needle 3, in the direction of lift. Valve-closure member 4, which is connected to valve needle 3, is lifted up from valve-seat surface 6, and fuel carried through fuel channels 30 a through 30 c is injected through injection orifice 7.

[0026] When the coil current is turned off; armature 20 drops back from internal pole 13 due to the pressure of restoring spring 23 after the magnetic field has declined sufficiently, so that first flange 21 which is connected to valve needle 3 moves against the direction of lift. Valve needle 3 is thus moved in the same direction, so that valve-closure member 4 is set down on valve-seat surface 6 and fuel injector 1 is closed.

[0027]FIG. 1B shows an enlarged view of area II in FIG. 1A in a sectional detail.

[0028] Constriction 26 between internal pole 13 and external pole 9, which acts as a magnetic throttle, is a potential mechanical weak point of fuel injector 1. Since fuel injector 1 is operated under high pressure, it is customary to reinforce constriction 26 with connecting component 29 so that fuel injector 1 is not deformed or damaged by the high pressure prevailing in the interior during operation.

[0029] Connecting component 29 is usually designed with an annular shape and surrounds internal pole 13 in the area of constriction 26 to stabilize fuel injector 1. In order for constriction 26 not to lose its effect as a magnetic throttle, connecting component 29 must be made of a material which is not ferritic.

[0030] Production and assembly of such a connecting component 29 is associated with additional costs and complexity, and furthermore, the mechanical weak point at constriction 26 may be damaged during the assembly of connecting component 29.

[0031] In a detail of a sectional view in the same area as FIG. 1B, FIG. 2 shows an embodiment of a fuel injector 1 according to the present invention. Identical components are labeled with the same reference numbers to facilitate a comparison.

[0032] Fuel injector 1 according to the present invention has a design similar to that of the fuel injector described in conjunction with FIG. 1A, so the following description is limited to the essential features.

[0033] Instead of having a constriction 26 between internal pole 13 and external pole 9, fuel injector 1 in the present embodiment has a tubular extension 35 of external pole 9, which is joined to internal pole 13 by a weld 36. Internal pole 13 and armature 20 pass through tubular extension 35 of external pole 9. Permanent magnets 34 run axially from an area of external pole 9 in which armature 20 is guided over working gap 27 to internal pole 13, which is situated in tubular extension 35 of external pole 9.

[0034] The arrangement of permanent magnets 34 on outer side 37 of external pole 9 yields a throttle effect which is produced by the opposite actions of the magnetic field of permanent magnets 34 and the magnetic field produced by solenoid 10. Permanent magnets 34 produce a locally limited magnetic flux, which claims a certain cross section in the material of tubular extension 35 of external pole 9 in contact with permanent magnets 34. Therefore, only a reduced cross section is available for the secondary flux when solenoid 10 is energized for actuation of fuel injector 1 and it rapidly approaches saturation, like constriction 26 between internal pole 13 and external pole 9 in fuel injector 1 according to the related art, as described in conjunction with FIGS. 1A and 1B, and therefore it acts as a magnetic throttle. Then a mechanical weak spot no longer exists.

[0035] Suitable materials for manufacturing the permanent magnets include substances having a high energy content, such as iron-neodymium-boron or compounds of cobalt with rare earth metals.

[0036] The polarity of permanent magnets 34 may be the same or opposite that of the magnetic field generated by solenoid 10. Permanent magnets 34 may be magnetized either before or after assembly on fuel injector 1.

[0037] Different variants are conceivable with regard to the shape and number of permanent magnets 34. In the simplest case, permanent magnet 34 may be designed as a closed ring which is placed on tubular extension 35 of external pole 9. Prefabricated solenoid 10 may be subsequently placed there.

[0038] To save on material and weight, the ring may be divided into several individual permanent magnets 34, which are in the form of annular segments having the same radius of curvature as tubular extension 35 of external pole 9. Almost any desired number of permanent magnets 34 may be used, but for reasons of symmetry there should be a certain minimum number, e.g., four. A rectangular segment shape is also conceivable.

[0039] Various mounting options are conceivable so that permanent magnets 34 in the form of rectangular and annular segments in particular will remain in the proper positions on the external pole.

[0040] First, permanent magnets 34 may be held directly on external pole 9 by their magnetic force due to the ferritic material. Secondly, adhesive bonds such as those formed by direct gluing or by fastening with double-sided adhesive tape may also be used. An extruded plastic sheathing on permanent magnets 34, which adhere magnetically to external pole 9, to better secure them is also possible.

[0041]FIG. 3 shows the embodiment of a fuel injector 1 according to the present invention, as illustrated in FIG. 2, on the basis of a schematic sectional diagram along line III-III in FIG. 2, as representative for the variants described above.

[0042] Armature 20, which is provided with at least one bore 30 a for fuel, is situated on valve needle 3. Armature 20 is guided in tubular extension 35 of external pole 9. In the present embodiment, four permanent magnets 34 in the form of annular segments separated by an equal number of recesses 38 are in contact with outside 37 of tubular extension 35. Permanent magnets 34 and recesses 38 between them cover approximately equal angular sections of approx. 45° each. Solenoid 10 is situated on permanent magnets 34 on the outside radially and is sealed from the outside by coil housing 11.

[0043] In addition to the throttle effect, permanent magnets 34 also offer the possibility of altering the properties of fuel injector 1 in a controlled manner when fuel injector 1 is completely assembled. In particular, it is possible to adjust the dynamic flow rate of fuel through fuel injector 1.

[0044] The present invention is not limited to the embodiments illustrated here and may also be used for any other designs of fuel injectors, e.g., for outwardly opening fuel injectors, or for other types of armatures, e.g., flat-type armatures. 

What is claimed is:
 1. A fuel injector (1), in particular an injector for direct injection of fuel into a combustion chamber of a mixture-compressing, spark-ignition internal combustion engine, having a solenoid (10), which cooperates with an armature (20), and having a magnetic internal pole (13) and a magnetic external pole (9), the armature (20) being connected in a force-locking manner with a valve needle (3) for actuating the fuel injector (1), the valve needle having on its injection end a valve-closure member (4), which cooperates with a valve seat (6), wherein at least one permanent magnet (34) is situated on a connecting area between the internal pole (13) and the external pole (9).
 2. The fuel injector according to claim 1, wherein the permanent magnet (34) is designed as a cylindrical ring and is situated on the external pole (9).
 3. The fuel injector according to claim 1, wherein multiple permanent magnets (34) designed in the form of annular segments are situated on the periphery of the external pole (9).
 4. The fuel injector according to claim 1, wherein multiple permanent magnets (34) designed in the form of rectangular segments are situated on the periphery of the external pole (9).
 5. The fuel injector according to one of claims 1 through 4, wherein the external pole (9) of the solenoid (10) has a tubular extension (35) in the direction of the internal pole (13).
 6. The fuel injector according to claim 5, wherein the tubular extension (35) wraps around the armature (20) and the internal pole (13).
 7. The fuel injector according to claim 6, wherein the at least one permanent magnet (34) abuts against an outer side (37) of the tubular extension (35).
 8. The fuel injector according to one of claims 1 through 7, wherein the at least one permanent magnet (34) is secured by its magnetic force to the outer side (37) of the tubular extension (35).
 9. The fuel injector according to one of claims 1 through 7, wherein the at least one permanent magnet (34) is secured by gluing to the outer side (37) of the tubular extension (35).
 10. The fuel injector according to claim 9, wherein the at least one permanent magnet (34) is secured by double-sided adhesive tape to the outer side (37) of the tubular extension (35).
 11. The fuel injector according to claim 9, wherein the at least one permanent magnet (34) is glued directly onto the outer side (37) of the tubular extension (35).
 12. The fuel injector according to one of claims 1 through 7, wherein the at least one permanent magnet (34) is secured by extrusion coating with plastic to the outer side (37) of the tubular extension (35).
 13. The fuel injector according to one of claims 1 through 12, wherein each permanent magnet (34) is magnetized before assembly.
 14. The fuel injector according to one of claims 1 through 13, wherein each permanent magnet (34) is made of a neodymium-iron-boron compound.
 15. The fuel injector according to one of claims 1 through 13, wherein each permanent magnet (34) is made of a rare earth-cobalt compound. 